It was a phone call that I didn’t want to receive. On a pleasant evening in June, a neighbor rancher – someone I’ve known for many years – phoned to ask my advice about some baleage. He had contracted for these bales from a friend’s field. When this baleage was made, however, it seems the tractor driver mowed close to the field’s perimeter and didn’t notice all the plants that were cut in the windrow. The forage was then baled and wrapped. Later that day, when my neighbor examined these bales, he noticed they contained a lot of plants that looked suspiciously like poison hemlock. Quite a lot. He called me that evening: Did I know exactly what poison hemlock looked like? And could he feed those bales safely to his cattle?
Oh, my. Poison hemlock is such a common plant around here. Well, perhaps I should describe it first.
What’s it look like?
Poison hemlock (Conium maculatum) is a member of the celery family, which also contains carrots, parsnip, dill and, of course, celery. (Poison hemlock is not related to hemlock trees in any way.) Poison hemlock is a tall, weedy, feathery-leafed plant with tiny white flowers. It can grow to 6 to 10 feet tall, but we often see it earlier in the season when it is much smaller. It has a hollow stem and a solid, fleshy, white taproot. Poison hemlock is a biennial plant, although it will sometimes act like a perennial under favorable conditions. It grows along roadsides, ditches, railroad tracks and the edges of fields. It’s more widespread than you would expect. Originally introduced from Europe, it’s now found in nearly every U.S. state and Canadian province, often as a common weed. I’ve even seen healthy stands of poison hemlock in city parks and along the edges of playing fields.
As you can imagine, accurate identification of this plant is critical. Young poison hemlock looks a lot like wild carrot (Daucus carota), also known as Queen Anne’s lace. Both plants have intricate fern-like leaves that spread flat on top in a shape vaguely resembling an umbrella. Both plants have tiny white flowers. And both plants like to grow in the same environments. But here are some very important differences: Wild carrot has a green stem, and its stem and leaves are slightly hairy (fuzzy, or the proper botanical term, pubescent). Wild carrot does not grow taller than 3 feet. And when you crush its leaves and flowers, they smell fresh and slightly sweet, a lot like, well, the tops of carrots.
Poison hemlock is quite different. Its stem and leaves are smooth, without hair, and its stem clearly shows purple spots or stripes, particularly near the base. (Its scientific species name maculatum means “spotted.”) And when you crush its leaves and flowers, they give off a slightly musty, unpleasant odor that smells a lot like mouse urine. (For those of you who know what mouse urine smells like.)
What’s it do?
Poison hemlock is a dangerous plant. It contains powerful toxins called piperidine alkaloids, which are found in all parts of the plant, sometimes as much as 1% of its dry weight. This plant actually contains eight different piperidine alkaloids. Two of the most common are coniine, which is more abundant in the flowers, and gamma-coniceine, which is more common in the stems and leaves. These alkaloids cause two types of toxic syndromes: neural paralysis and congenital deformities.
The neural syndrome is more widely known and feared. Within a few hours of consuming a small amount of leaves – only a few ounces for sheep and less than a pound for cattle – the poor animal becomes increasingly nervous, then shows trembling and incoordination, with frequent urination and defecation. Its pupils dilate, its pulse becomes shallow, and a coldness spreads to its extremities. Finally, the animal sinks into a coma, suffers respiratory paralysis and dies of acute respiratory failure.
Interestingly, animals differ in their sensitivities to these toxins. Cattle are the most sensitive, followed by horses, sheep and hogs, in that order, probably because of how well their livers convert the toxins into safe compounds for excretion. In this case, apparently, cattle are not as good as sheep.
Neither are humans. People have known about poison hemlock for thousands of years. In fact, the ancient Greeks routinely used poison hemlock to execute criminals, kind of like a lethal injection without the injection. The most famous case, of course – for those of you who recall your Plato – was Socrates in 399 B.C. The Athenian rulers apparently considered Socrates a danger to the state and ordered him to drink tea made from poison hemlock. Although Plato was not a trained toxicologist, he had an acute eye for detail and described Socrates’ symptoms very accurately, including the progressive coldness in his arms and legs.
Photo by Woody Lane.
So if you encounter a carrot-like plant that is 8 feet tall, with purple stripes on its lower stem, with crushed leaves that smell like a mouse nest, don’t eat it. Even if it’s only 3 feet tall and looks a lot like Queen Anne’s lace, don’t eat it. Some people do, and every year there are reports of hikers and picnickers who mistook its leaves for parsley or its roots for wild parsnip. Remember that all parts of this plant are toxic. Even children who have used its hollow stem to make tiny whistles have been poisoned. And here’s the worst news: There is no direct antidote for this toxin.
Poison hemlock also causes a lesser-known toxicity: It can damage fetuses (teratogenic effects), particularly in cattle and hogs. If pregnant cows consume poison hemlock between 55 and 75 days of gestation (and manage to survive), their calves will be born with skeletal deformities almost indistinguishable from the crooked calf disease caused by toxic lupines. Again, livestock species are different in their susceptibility to these toxic teratogenic effects. Horses and sheep rarely show these symptoms.
Enough background description. We generally don’t serve poison hemlock tea to our livestock (I hope), so how does all this background information relate to the real world of farms and ranches? Like the situation faced by my neighbor.
For grazing animals, poison hemlock is generally not a serious problem. Animals don’t like the plant and will avoid it, unless they are desperate and starving and totally out of feed. There is one classic exception, however: Young livestock like calves and lambs in early spring. These naïve animals like to explore and haven’t yet learned good nutritional sense from their mothers. In the spring, young hemlock plants are short, green and succulent, and these animals don’t know any different, so they eat some …
What about hay and silage?
Yes, hay containing poison hemlock can be quite toxic, and there are hundreds of veterinary case reports that describe livestock poisonings by contaminated hay. But these piperidine alkaloids are slightly volatile, which means that some of the molecules will escape as gas during the drying process, thus reducing the toxicity. In addition, if animals are given a chance to sort through dry hay, they will often avoid the unpalatable hemlock. So, theoretically, if they aren’t starving or forced to eat everything, they can potentially eat around the problem. But not always. And if a farmer decides to “save waste” by pelleting the hay, then those pellets contain everything in the hay, giving the animals no choice.
But of the three feeding options – grazing, hay and silage – it’s silage that may potentially represent the worst scenario. The piperidine alkaloids are not destroyed or reduced by the ensiling process. They don’t lose their toxicity. And some characteristics of silage may make the situation worse. Properly made silage is usually quite palatable to livestock. Its sweet taste can mask the unpleasant taste of the hemlock. Also, animals can’t sort through silage as easily as hay and are therefore more likely to consume forage that includes toxic plant material.
So what happened with my neighbor and all those bales of wrapped baleage? He decided to be on the safe side and not use them for cattle feed. Those bales are still in the field. Waiting, perhaps, for the next ice age or whatever. Or we might unwrap them and make compost from that forage. I know the veterinary school at Cornell University maintains a demonstration garden of toxic plants. Perhaps we can send our compost there.
